1. Field of the Invention
The present invention relates to disk drive devices to drive an information recording disk such as a magnetic disk.
2. Description of Related Art
The hard disk drives (HDDS) have widely spread as an external storage device for a personal computer. Meanwhile, the HDD has been reduced in price as the recording density has increased, and today, some home electric appliances have an internal HDD. The HDD can store a considerable amount of video and music contents and various products with an HDD are on the way to the market. Car audio equipment is a prospective item to be provided with an HDD. Car navigation systems mainly use DVDs as the storage, while the use of HDD is expected in the future.
The basic construction of an HDD is shown in FIG. 1. The shown HDD is a ramped loading type device in which a magnetic head 51 provided at a tip end of an actuator 54 is mechanically raised from the magnetic disk surface to float.
As shown, the magnetic head 51 attached to the actuator 54 is provided movably in the radial direction (denoted by the arrow) of the magnetic disk 53 and positioned by a voice coil motor (VCM) 160. The magnetic head 51 is pressed against the surface of the magnetic disk 53 by the elasticity of a suspension 57. Meanwhile, the rotation of the magnetic disk 53 controls the distance between the disk surface of magnetic disk 53 and the magnetic head 51 to be several tens pm by the aerodynamic floatation acting upon the magnetic head 51. In an inactive state, the magnetic head 51 is positioned at a retreat position where the head 51 is placed over the tapered portion 56 of a ramp 55 formed at one end of a casing frame 50.
The positional relation between the magnetic head 51 and the ramp 55 is shown in a sectional view in FIG. 2. As shown, the ramp 55 positioned in the vicinity of the outer circumference of the magnetic disk 53 has the tapered portion 56 gradually tapered height-wise, outward in the radial direction of the disk from the surface of the magnetic disk 53. The magnetic head 51 is positioned at a location a at a prescribed distance from the main surface of the magnetic disk 53 at the time of reading/writing information from/to the magnetic disk 53 (at the time of driving). In an inactive state (unloaded state), the head is placed over the tapered portion 56 as denoted by the arrow in the figure, regains a retreat position, i.e., a home position b and stands by.
The above described HDD has a function called “emergency unloading.” By the emergency unloading function, the head 53 is forcibly moved to the retreat position, i.e., the home position. This is carried out in order to prevent the magnetic disk 53 from being damaged by the head when the power supply voltages to a spindle motor 52 and a motor for driving the magnetic head 51 are significantly lowered. A power supply is necessary to carry out this emergency unloading function. Meanwhile, according to one known technique, counter electromotive force, in other words, no-loaded electromotive force generated by the inertial rotation of the spindle motor 52 is used to perform the operation when the power supplies are both down as described above.
When this technique is applied to a disk drive device mounted in an engine driven vehicle, as the battery voltage significantly drops at the start of the engine, the above emergency unloading operation is performed each time the engine is started.
FIG. 3 shows an example of a power supply circuit in an engine driven vehicle. More specifically, an alternator G is driven by an engine which is not shown. An alternate power supplied from the alternator G is rectified and smoothed by a rectifier D and supplied to a battery B. The battery voltage Vb of the battery B is supplied to a movable terminal m of an engine key switch SW. The engine key switch SW has fixed terminals ACC, ON and ST, and the battery voltage Vb passed through the terminal ACC is supplied to a light load such as audio equipment as an ACC power supply. The battery voltage Vb passed through the terminal ON is supplied to a heavy load HL such as a power window as an ON power supply. The battery voltage Vb passed through the terminal ST is supplied to a starting motor which is not shown as an MST voltage and rotates the starting motor for starting the engine. Meanwhile, the battery voltage Vb is supplied to the light load LL as a backup power supply through a line BU.
FIGS. 4A and 4B are timing charts showing how a voltage on a power supply lines changes at the start of the engine. FIG. 4A shows how the backup power supply voltage changes, while FIG. 4B shows how the ACC voltage changes. The timings (I), (II), (III) and (IV) as shown correspond to positions of the key switch of the engine key. In the timing (I), the engine key is at the “ACC position” where power is supplied to a light load such as audio equipment. In the timing (II), the engine key is at the “ON position” where power is supplied to a heavy load such as a power window. In the timing (III), the key switch is in the “ST position” where power is supplied to the starting motor. In the timing (IV), the starting motor has started and the engine key regains the “ON position.”
During the operation, at the start of the engine, a drop in the battery voltage could cause a drop not only in the ACC voltage but also the backup power supply voltage (during the period from (III) to (IV) in FIG. 4).
Therefore, if an HDD is provided in an engine-driven vehicle, a possible drop in the power supply voltage at the start of the engine is likely to cause the above described emergency unloading every time the engine is started. In the emergency unloading operation, the counter electromotive force of a spindle motor is used to force the head to move. Therefore, in products for vehicles, the magnetic head 51 more often collides with the tapered portion 56 of the ramp 55 before the head 51 reaches the stand-by position b of the ramp 55 than the case of other kinds of products such as personal computers. More specifically, in the HDD for vehicle, the ramp 55 and the magnetic head 51 must have higher durability. This is a common disadvantage among disk drive devices operated with unstable power supply voltages.